The driving method known as amplitude selective addressing has been conventionally used to drive passive-matrix display devices. The 6-level driving method is most commonly used of the methods categorized as amplitude selective addressing. An example of the 6-level driving method is given in Japanese Patent Application Laid-open No. Hei2-89. The 6-level driving method will now be explained with reference to FIGS. 23 through 25C.
FIG. 23 shows the configuration and display components of a liquid crystal display panel. The figure shows a liquid crystal display panel 300 comprising a liquid crystal layer (not shown) and a pair of substrates 302 and 304, sandwiching the liquid crystal layer. Scanning electrodes Y1-Y6 are formed horizontally within substrate 302. The other substrate 304 contains signal electrodes X1-X6. Pixels are formed at intersections between scanning electrodes Y1-Y6 and signal electrodes X1-X6. In FIG. 23, on-status pixels are shown with hatching, and off-status pixels are shown without hatching.
The liquid crystal display panel 300 shown in FIG. 23 has only 6.times.6 pixels in order to simplify the explanation. The number of pixels in liquid crystal display panels in actual use will normally be far greater than this.
Either a selection voltage or non-selection voltage is applied in sequential order to each of the scanning electrodes Y1 to Y6. The period required to apply the selection voltage once to each of the scanning electrodes Y1-Y6 is called one frame.
At the same time as when either a selection voltage or non-selection voltage is applied to each of the scanning electrodes Y1-YG, either an on-voltage or off-voltage is applied to each of the signal electrodes X1-X6. That is, in order to turn on a pixel at an intersection between a scanning electrode and a signal electrode, an on-voltage is applied to the signal electrode when the scanning electrode is selected. In order not to turn on the pixel, an off-voltage is applied to the signal electrode when the scanning electrode is selected.
FIGS. 24A, 24B, 240, and FIGS. 25A, 25B, 25C show examples of driving voltage (applied voltage) waveforms.
FIGS. 24A, 24B, and 24C respectively show a signal voltage waveform applied to signal electrode X5, a scanning voltage waveform applied to scanning electrode Y3, and a voltage waveform applied to a pixel (on-status) at the intersection between signal electrode X5 and scanning electrode Y3.
Also, FIGS. 25A, 25B, and 25C respectively show a signal voltage waveform applied to signal electrode X5, a scanning voltage waveform applied to scanning electrode Y4, and a voltage waveform applied to a pixel (off-status) at the intersection between signal electrode X5 and scanning electrode Y4.
In FIGS. 24A, 24B, 24C, 25A, 25B, and 250, both F1 and F2 indicate one frame.
In the frame F1,
selection voltage=V0, non-selection voltage=V4 PA1 on-voltage=V5, off-voltage=V3 PA1 selection voltage=V5, non-selection voltage=V1 PA1 on-voltage=V0, off-voltage=V2 PA1 V0-V1=V1-V2=V PA1 V3-V4=V4-V5=V PA1 V0-V5=k.V (k; positive number). PA1 a liquid crystal display panel having a liquid crystal layer sandwiched by a plurality of scanning electrodes and a plurality of signal electrodes; PA1 a first voltage applying means which applies a scanning voltage consisting of selection and non-selection voltages to a plurality of scanning electrodes of said liquid crystal display panel; PA1 a second voltage applying means which applies a signal voltage consisting of on-voltage and off-voltage to a plurality of signal electrodes of said liquid crystal display panel; PA1 a polarity inversion control means, connected to said first voltage applying means and said second voltage applying means, to control the polarity inversion of the driving voltage, which is the potential difference between said scanning electrode and said signal electrode, corresponding to the on/off-status of each pixel of said liquid crystal display panel; and, PA1 said liquid crystal display panel driven by an AC driver. PA1 a liquid crystal display panel having a liquid crystal layer sandwiched by a plurality of scanning electrodes and a plurality of signal electrodes; PA1 a first voltage applying means which applies a scanning voltage consisting of selection and non-selection voltages to the plurality of scanning electrodes of said liquid crystal display panel; PA1 a second voltage applying means which applies a signal voltage consisting of on-voltage and off-voltage to a plurality of signal electrodes of said liquid crystal display panel; PA1 a polarity inversion means, connected to said first voltage applying means and said second voltage applying means, to control the polarity inversion of the driving voltage, which is the potential difference between said scanning electrode and said signal electrode, corresponding to the on/off-status of each pixel of said liquid crystal display panel; PA1 and that images are displayed on said liquid crystal display.
in the frame F2,
where,
Thus the system is AC driven, through the polarity being inverted between frame F1, and frame F2.
Also, a 6-level driving method whereby the polarity is periodically switched in intervals other than those corresponding to frames F1 and F2 is disclosed in Japanese Patent Application Laid-open No. Sho62-31825.
An alternative to the 6-level driving method is the so called IHAT method. This method, proposed by T. N. Ruckmongathan, makes driving at low voltages possible and enables display uniformity to be achieved (1988 International Display Research Conference). In this driving method, N lines of line electrodes are bundled to p (p=N/M) groups of subgroups, each of which consists of M lines of line electrodes selected together. This method is disclosed in Japanese Patent Application Laid-open No. Hei5-46127.
Incidentally, driving a liquid crystal display panel by such methods as the aforementioned 6-level driving method and the IHAT method may require significant power consumption depending on the pattern of characters, figures, and the like displayed by the panel.
For example, consider scanning electrode Y1 in the liquid crystal display panel 300 shown in FIG. 23. If the scanning electrode Y1 is not selected during a frame period F1, non-selection voltage V4 is applied to the scanning electrode Y1. As the scanning electrode that will have a selection voltage applied shifts from Y2 through to Y6 (hereafter, "the selected scanning electrode"), on-voltage V5 and off-voltage V3 will be applied alternately and repeatedly to signal electrodes X1-X4, and X6. Therefore, in the period when scanning electrode Y1 is not selected, voltages -V and +V will be applied alternately to each pixel at the intersections of scanning electrode Y1 and signal electrodes X1-X4, and X6.
In addition, because the scanning electrodes Y1-Y6, and signal electrodes X1-X4, X6 have a set width, and the liquid crystal layer between them acts as a dielectric, each pixel is electrically equivalent to a capacitor. Therefore, the aforementioned alternating voltage will be applied to these capacitors, which results in power being consumed by the power supply circuit driving the liquid crystal display panel 300.
An increase in power consumption will not only be observed when pixels repeatedly alternate between on-status and off-status during a frame period, but also whenever the polarity is changed in a frame.
Also, any methods which utilize conventional amplitude selective addressing may generate display unevenness depending on the patterns of characters and figures displayed on the liquid crystal display panel, as well as the aforementioned possible increase in power consumption. The IHAT method does improve the situation somewhat, though it does not completely eliminate display unevenness regardless of the patterns displayed.
In short, when the liquid crystal display panel 300 is driven by an amplitude selective addressing scheme, the voltage waveforms applied to pixels are not as ideal as the rectangular waves shown in FIGS. 24A through 25C. The first reason for this is the capacitance of each pixel, which is determined by the area of the pixel, the thickness of the liquid crystal layer, and the dielectric constant of the liquid crystal material. The second reason for this is that both the scanning and signal electrodes are made of transparent conductor films, which naturally have a certain level of electric resistance, generally with a sheet resistance of the order of dozens of ohms.
For these reasons therefore, even if an ideal rectangular waveform voltage as shown by FIGS. 24A through 25C is applied to the liquid crystal display panel 300, the actual voltage waveform applied to each pixel will be distorted somewhat. As a result, the effective voltage of the waveform applied to the pixels will vary, thus causing contrast unevenness.
This problem has been known for some time, and driving methods other than that disclosed in the aforementioned Japanese Patent Application Laid-open No. Sho62-31825 are disclosed in Japanese Patent Application Laid-open Nos. Sho60-19196 and Hei2-89.
In light of the problems inherent in conventional technologies, the present invention has been devised to provide a liquid crystal display panel driving method, a liquid crystal display device and electronic equipment using the same characterized by low power consumption and suppressed display unevenness.